We'll talk about the hidden sugar in healthy foods. Turns out Greek yogurt packed with protein can also be packed with sugar. Becky Worley has the story. Reporter: In the quest to stay healthy, losing a few pounds frequently comes down to simple math, less fat, less sugar, more protein and a secret weapon for many in the weight loss war is Greek yogurt. It's high in protein. It's got pro-buy Ott ticks, it's lower in sugar than regular yogurt so it's just a good energy boosting food. Reporter: But in recent testing, popular brands, "Consumer reports" was suffered. When we looked at the nutrition labels we noticed something a little strange about the whole food product. Reporter: Whole foods, 365 plain fat-free Greek yogurt says on the label it has two grams of sugar per serving. But all other brands of the same type have 6 to 12 grams of sugar. Tastes the same as all the other plain nonfat Greek yogurts. None of these are any sweeter than the whole foods brand. To have two grams of sugar in a cup of yogurt is a little unusual even though it's a plain yogurt. Reporter: So "Consumer reports" sent six different samples to an independent lab that conducted industry standard tests to determine the sugar content. Instead of two grams of sugar like the label listed, "Consumer reports" says the lab found the average sugar content was 11.4 grams. More than five times the listed amount. A big deal to some. Consumers like a diabetic would be looking at that nutrition label making decisions for their daily life and intake and if they're counting sugar grams every gram counts for them. Reporter: Whole foods told us this product was tested by a reputable third party lab using fda approved testing methodology to determine the labeling. They say they recognize that "Consumer reports" is a trusted publication and are looking into why their test results differ. So while this Greek yogurt drama plays out, everyone should remember -- Get a plain nonfat Greek yogurt and add your own level of sweetness so you own the power how much sugar is getting added this there. Reporter: For "Good morning America," Becky Worley, ABC news, Oakland, California.

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